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Abstract:

Disclosed herein is a control apparatus, including: a supplying section
to which a voltage which varies in response to a variation of a state is
supplied from an electric power generation section; and a control section
configured to change the number of battery units, for which charging is
to be carried out, in response to a relationship between the voltage and
a reference value.

Claims:

1. A control apparatus, comprising: a supplying section to which a
voltage which varies in response to a variation of a state is supplied
from an electric power generation section; and a control section
configured to change the number of battery units, for which charging is
to be carried out, in response so a relationship between the voltage and
a reference value.

2. The control apparatus according to claim 1, wherein the control
section increases the number of battery units when the voltage is higher
than the reference value but decreases the number of battery units when a
state in which the voltage is equal to or lower than the reference value
continues for a predetermined period of time.

3. The control apparatus according to claim 1, wherein the control
section calculates first electric power when the voltage is equal to or
lower than the reference value and decreases the number of battery units
when the first electric power is higher than power consumption of a
charging controlling section which the battery units have, and calculates
second electric power when the voltage is higher than the reference value
and increases the number of battery units when the second electric power
is higher than the power consumption of the charging controlling section
which the battery units have.

4. The control apparatus according to claim 3, wherein the first electric
power is a difference between the electric power supplied from the
electric power generation section and total electric power of the battery
units when the number of battery units is decreased, and the second
electric power is a difference between the power supplied form the
electric power generation section and the total electric power by the
battery units.

5. The control apparatus according to claim 1, wherein the electric power
generation section is configured from a photovoltaic power generation
section.

6. A control method, comprising: supplying a voltage, which varies in
response to a variation of a state, from an electric power generation
section; and changing the number of battery units, for which charging is
to be carried out, in response to a relationship between the voltage and
a reference value.

Description:

BACKGROUND

[0001] The present disclosure relates to a control apparatus and a control
method for carrying out charging control, for example, into a battery
unit.

[0002] In recent years, in order to enhance the output capacity, a
plurality of power supply modules are connected in parallel such that
electric power is supplied from each of the power supply modules. For
example, Japanese Patent Laid-Open No 2006-034047 discloses a power
supply apparatus which includes a plurality of power supply units
connected in parallel such that they are started up successively.

SUMMARY

[0003] The power supply units of the power supply apparatus disclosed in
the document mentioned above generate a voltage from a fixed input, and
the power supply apparatus has a problem in that the power supply units
cannot be charged.

[0004] Therefore, it is desirable to provide a control apparatus and a
control method by which charging control into one or a plurality of
battery units is carried out.

[0005] According to an embodiment of the present disclosure, there is
provided a control apparatus including a supplying section to which a
voltage which varies in response to a variation of a state is supplied
from an electric power generation section, and a control section
configured to change the number of battery units, for which charging is
to be carried out, in response to a relationship between the voltage and
a reference value.

[0006] According to another embodiment of the present disclosure, there is
provided a control method including supplying a voltage, which varies in
response to a variation of a state, from an electric power generation
section, and chan ing the number of battery units, for which charging is
to be carried out, in response to a relationship between the voltage and
a reference value.

[0007] With at least one of the embodiments, charging control for one or a
plurality of battery units can be carried out efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a block diagram showing an example of a configuration of
a system;

[0009] FIG. 2 is a block diagram showing an example of a configuration of
a control unit;

[0010] FIG. 3 is a block diagram showing an example of a configuration of
a power supply system of the control unit;

[0011] FIG. 4 is a circuit diagram showing an example of a particular
configuration of a high voltage input power supply circuit of the control
unit;

[0012] FIG. 5 is a block diagram showing an example of a configuration of
a battery unit;

[0013] FIG. 6 is it block diagram showing an example of a configuration of
a power supply system of the battery unit;

[0014] FIG. 7 is a circuit diagram showing an example of a particular
configuration of a charger circuit of the battery unit;

[0015]FIG. 8A is a graph illustrating a voltage-current characteristic of
a solar cell, and FIG. 8B is a graph, particularly a PV curve,
representative of a relationship between the terminal voltage of the
solar cell, and the generated electric power of the solar cell in the
case where a voltage-current characteristic of the solar cell is
represented by a certain curve;

[0016]FIG. 9A is a graph illustrating a variation of an operating point
with respect, to a change of a curve representative of a voltage-current
characteristic of a solar cell, and FIG. 95 is a block diagram showing an
example of a configuration of a control system wherein cooperation
control is carried out by a control unit and a plurality of battery
units;

[0017] FIG. 10A is a graph illustrating a variation of an operating point
when cooperation control is carried out in the case where the
illumination intensity upon a solar cell decreases, and FIG. 105 is a
graph illustrating a variation of an operating point when cooperation
control is carried out in the case where the load as viewed from the
solar cell increases;

[0018] FIG. 11 is a graph illustrating a variation of an operating point
when cooperation control is carried out in the case where both of the
illumination intensity upon the solar cell and the load as viewed from
the solar cell vary;

[0019] FIG. 12 is a graph illustrating an example of a change of an
operating point when both of the illumination intensity upon the solar
cell and the load as viewed from the solar cell vary;

[0020] FIG. 13 is a flow chart illustrating an example of a flow of
processing of a first unit number controlling process;

[0021] FIGS. 14 and 15 are views illustrating different examples of a
second unit number controlling process; and

[0022] FIG. 16 is a flow chart illustrating an example of a flow of
processing of the second unit number controlling process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] In the following, an embodiment of the present disclosure is
described with reference to the accompanying drawings. It is to be noted
that the description is given in the following order.

<1. Embodiment>

<2. Modifications>

[0024] It is to be noted that the embodiment and the modifications
described below are specific preferred examples of the present
disclosure, and the present disclosure is not limited to the embodiment
and the modifications.

1. Embodiment

[Configuration of the System]

[0025] FIG. 1 shows an example of a configuration of a control system
according to the present disclosure. The control system is configured
from one or a plurality of control units CU and one or a plurality of
battery units BU. The control system 1 shown as an example in FIG. 1
includes one control unit CU, and three be units BUa, BUb and BUc. When
there is no necessity to distinguish the individual battery units, each
battery unit is suitably referred to as battery unit BU.

[0026] In the control system 1, it is possible to control the battery
units BU independently of each other. Further, the battery units BU can
be connected independently of each other in the control system 1. For
example, in a state in which the battery unit BUa and the battery unit
BUb are connected in the control system 1, the battery unit BUc can be
connected newly or additionally in the control system 1. Or, in a state
in which the battery units BUa to BUc are connected in the control system
1, it is possible to remove only the battery unit BUb from the control
system. 1.

[0027] The control unit CU and the battery units BU are individually
connected to each other by electric power lines. The power lines include,
for example, an electric power line L1 by which electric power is
supplied from the control, unit CU to the battery units BU and another
electric power line L2 by which electric power is supplied from the
battery units BU to the control unit CU. Thus, bidirectional
communication is carried out through a signal line SL between the control
unit CU and the battery units BU. The communication may be carried out in
conformity with such specifications as, for example, the SMBus (System
Management Bus) or the UART (Universal Asynchronous
Receiver-Transmitter).

[0028] The signal line SL is configured from one or a plurality of lines,
and a line to be used is defined in accordance with an object thereof.
The signal line SL is used commonly, and the battery units BU are
connected to the signal line SL. Each battery unit BU analyzes the header
part of a control signal transmitted thereto through the signal line SL
to decide whether or not the control signal is destined for the battery
unit BU itself. By suitably setting the level and so forth of the control
signal, a command to the battery unit BU can be transmitted. A response
from a battery unit BU to the control unit CU is transmitted also to the
other battery units BU. However, the other battery units BU do not
operate in response to the transmission of the response. It is to be
noted that, while it is assumed that, in the present example,
transmission of electric power and communication are carried out by means
of wires, they may otherwise be carried out by radio.

[General Configuration of the Control Unit]

[0029] The control unit CU is configured from a high voltage input power
supply circuit 11 and a low voltage input power supply circuit 12. The
control unit CU has one or a plurality of first devices. In the present
example, the control unit CU has two first devices, which individually
correspond to the high voltage input power supply circuit 11 and the low
voltage input power supply circuit 12. It is to be noted that, although
the terms "high voltage" and "low voltage" are used herein, the voltages
to be inputted to the high voltage input power supply circuit 11 and the
low voltage input power supply circuit 12 may be included in the same
input range. The input ranges of the voltages which can be accepted by
the high voltage input power supply circuit 11 and the low voltage input
power supply circuit 12 may overlap with each other.

[0030] A voltage generated by an electric power generation section which
generates electricity in response to the environment is supplied to the
high voltage input power supply circuit 11 and the low voltage input
power supply circuit 12. For example, the electric power Generation
section is an apparatus which generates electricity by the sunlight or
wind power. Meanwhile, the electric power generation section is not
limited to that apparatus which generates electricity in response the
natural environment. For example, the electric power generation section
may be configured as an apparatus which generates electricity by human
power. Although an electric generator whose power generation energy
fluctuates in response to the environment or the situation is assumed in
this manner, also that electric generator whose power generation energy
does not fluctuate is applicable. Therefore, as seen in FIG. 1, also AC
power can be inputted to the control system 1. It is to be noted that
voltages are supplied, from the same electric power generation section or
different electric power generation sections to the high voltage input
power supply circuit 11 and the low voltage input power supply circuit
12. The voltage or voltages generated by the electric power generation
section or sections are an example of a first voltage or voltages.

[0031] To the high voltage input, power supply circuit 11, for example, a
DC (Direct Current) voltage V10 of approximately 75 to 100 V (volts)
generated by photovoltaic power generation is supplied. Alternatively, an
AC (Alternating Current) voltage of approximately 100 to 250 V may be
supplied to the high voltage input power supply circuit 11. The high
voltage input power supply circuit 11 generates a second voltage in
response to a fluctuation of the voltage V10 supplied thereto by
photovoltaic power generation. For example, the voltage V10 is stepped
down by the high voltage input power supply circuit 11 to generate the
second voltage. The second voltage is a DC voltage, for example, within a
range of 45 to 48 V.

[0032] When the voltage V10 is 75 V, the high voltage input power supply
circuit 11 converts the voltage V10 into 45 V. However, when the voltage
V10 is 100 V, the high voltage input rower supply circuit 11 converts the
voltage V10 into 48 V. In response to a variation of the voltage V10
within the range from 75 to 100 V, the high voltage input power supply
circuit 11 generates the second voltage such that the second voltage
changes substantially linearly within the range from 45 to 48 V. The high
voltage input power supply circuit 11 outputs the generated second
voltage. It is to be noted that the rate of change of the second voltage
need not necessarily be linear, but a feedback circuit may be used such
that the output of the high voltage input power supply circuit 11 is used
as it is.

[0033] To the low voltage input rower supply circuit 12, a DC voltage V11
within a range of 10 to 40 V generated, for example, by electric power
generation by wind, or electric power generation by human power is
supplied. The low voltage input power supply circuit 12 generates a
second voltage in response to a fluctuation of the voltage V11 similarly
to the high voltage input power supply circuit 11. The low voltage input
power supply circuit 12 steps up the voltage V11, for example, to a DC
voltage within the range of 45 to 49 V in response to a change of the
voltage V11 within the range from 10 V to 40 V. The stepped up DC voltage
is outputted from the low voltage input power supply circuit 12.

[0034] Both or one of the output voltages of the high voltage input power
supply circuit 11 and the low voltage input power supply circuit 12 is
inputted to the battery units BU. In FIG. 1, the DC voltage supplied to
the battery units BU is denoted by V12. As described hereinabove, the
voltage V12 is, for example, a DC voltage within the range from 45 to 48
V. All or some of the battery units BU are charged by the voltage V12. It
is to be noted that a battery unit BU which is discharging is not
charged.

[0035] A personal computer may be connectable to the control unit CU. For
example, a USE (Universal Serial Bus) cable is used to connect the
control unit CU and the personal computer to each other. The control unit
CU may be controlled using the personal computer.

[General Configuration of the Battery Unit]

[0036] A general configuration of a battery unit which is an example of a
second apparatus is described. While description is given below taking
the battery unit BUa as an example, unless otherwise specified, the
battery unit BUb and the battery unit BUc have the same configuration.

[0037] The battery unit BUa includes a charger or charging circuit 41a, a
discharger or discharging circuit 42a and a battery Ba. Also the other
battery units BU include a charger or charging circuit, a discharger or
discharging circuit and a battery. In the following description, when
there is no necessity to distinguish each battery, it is referred to
suitably as battery B.

[0038] The charger circuit 41a converts the voltage V12 supplied thereto
from the control unit CU into a voltage applicable to the battery Ba. The
battery Ba is charged based on the voltage obtained by the conversion. It
is to be noted that the charger circuit. 41a chances the charge rate into
the battery Ba in response to a fluctuation of the voltage V12.

[0039] Electric power outputted from the battery Ba is supplied to the
discharger circuit 42a. From the battery Ba, for example, a DC voltage
within a range from substantially from 12 to 55 V is outputted. The DC
voltage supplied from the battery Ba is converted into a DC voltage V13
by the discharger circuit 42a. The voltage V13 is a DC voltage of, for
example, 48 V. The voltage V13 is outputted from the discharger circuit
42a to the control unit CU through the electric power line L2. It is to
be noted that the DC voltage outputted from the battery Ba may otherwise
be supplied directly to an external apparatus without by way of the
discharger circuit 42a.

[0040] Each battery B may be a lithium-ion battery, an olivine-type iron
phosphate lithium-ion battery, a lead battery or the like. The batteries
B of the battery units BU may be those of different battery types from
each other. For example, the battery Ba of the battery unit BUa and the
battery Bb of the battery unit BUb are configured from a lithium-ion
battery and the battery Bc of the battery unit BUc is configured from a
lead battery. The number and the connection scheme of battery cells in
the batteries B can be changed suitably. A plurality of battery cells may
be connected in series or in parallel. Or series connections of a
plurality of battery cells may be connected in parallel.

[0041] When the battery units discharge, in the case where the load is
light, the highest one of the output voltages of the battery units is
supplied as the voltage V13 to the electric power line L2. As the load
becomes heavier, the outputs of the battery units are combined, and the
combined output is supplied to the electric power line L2. The voltage
V13 is supplied to the control unit CU through the electric power line
L2. The voltage V13 is outputted from an output port of the control unit
CU. To the control unit CU, electric power can be supplied in a
distributed relationship from the battery units BU. Therefore, the burden
on the individual battery units BU can be moderated.

[0042] For example, the following use form may be available. The voltage
V13 outputted from the battery unit BUa is supplied to an external
apparatus through the control unit CU. To the battery unit BUb, the
voltage V12 is supplied from the control unit CU, and the battery Bb of
the battery unit BUb is charged. The battery unit BUc is used as a
redundant power supply. For example, when the remaining capacity of the
battery unit BUa drops, the battery unit to be used is changed over from
the battery unit BUa to the battery unit BUc and the voltage V13
outputted from the battery unit BUc is supplied to the external
apparatus. Naturally, the use form described is an example, and the use
form of the control, system 1 is not limited to this specific use form.

[Internal Configuration of the Control Unit]

[0043] FIG. 2 shows an example of an internal configuration of the control
unit CU. As described hereinabove, the control unit CU includes the high
voltage input power supply circuit 11 and the low voltage input power
supply circuit 12. Referring to FIG. 2, the high voltage input power
supply circuit 11 includes an AC-DC converter 11 for converting an AC
input to a DC output, and a DC-DC converter 11b for stepping down the
voltage V10 to a DC voltage within the range from 45 to 48 V. The AC-DC
converter 11 and the DC-DC converter 11b may be Those of known types. It
is to be noted that, in the case where only a DC voltage is supplied to
the high voltage input power supply circuit 11, the AC-DC converter 11
may be omitted.

[0044] A voltage sensor, an electronic switch and a current sensor are
connected to each of an input stage and an output stage of the DC-DC
converter 11b. In FIG. 2 and also in FIG. 5 hereinafter described, the
voltage sensor is represented by a square mark; the electronic switch by
a round mark; and the current sensor by a round mark with slanting lines
individually in a simplified representation. In particular, a voltage
sensor 11c, an electronic switch 11d and a current sensor 11e are
connected to the input stage of the DC-DC converter 11b. A current sensor
11f, an electronic switch 11g and a voltage sensor 11h are connected to
the output stage of the DC-DC converter 11b. Sensor information obtained
by the sensors is supplied to a CPU (Central Processing Unit) 13
hereinafter described. On/off operations of the electronic switches are
controlled by the CPU 13.

[0045] The low voltage input power supply circuit 12 includes a DC-DC
converter 12a for stepping up the voltage V11 to a DC voltage within the
range from 45 to 48 V. A voltage sensor, an electronic switch and a
current sensor are connected to each of an input stage and an output
stage of the low voltage input power supply circuit 12. In particular, a
voltage sensor 12b, an electronic switch 12c and a current sensor 12d are
connected to the input stage of the DC-DC converter 12a. A current sensor
12e, an electronic switch 12f and a voltage sensor 12g are connected to
the output stage of the DC-DC converter 12a. Sensor information obtained
by the sensors is supplied to the CPU 13. On/off operations of the
switches are controlled by the CPU 13.

[0046] It is to be noted that, in FIG. 2, an arrow mark extending from a
sensor represents that sensor information is supplied to the CPU 13. An
arrow mark extending to an electronic switch represents that the
electronic switch is controlled by the CPU 13.

[0047] An output voltage of the high voltage input power supply circuit 11
is outputted through a diode. An output voltage of the low voltage input
power supply circuit 12 is outputted through another diode. The output
voltage of the high voltage input power supply circuit 11 and the output
voltage of the low voltage input power supply circuit 12 are combined,
and the combined voltage V12 is outputted to the battery unit BU through
the electric power line L1. The voltage V13 supplied from the battery
unit BU is supplied to the control, unit CU through the electric power
line L2. Then, the voltage V13 supplied to the control unit CU is
supplied to the external, apparatus through an electric power line L3. It
is to be noted that, in FIG. 2, the voltage supplied to the external
apparatus is represented as voltage V14.

[0048] The electric power line L3 may be connected to the battery units
BU. By this configuration, for example, a voltage outputted from the
battery unit BUa is supplied to the control unit CU through the electric
power line P2. The supplied voltage is supplied to the battery unit BUb
through the electric power line L3 and can charge the battery unit BUb.
It is to be noted that, though not shown, power supplied to the control
unit CU through the electric power line L2 may be supplied to the
electric power line L1.

[0049] The control unit CU includes the CPU 13. The CPU 13 controls the
components of the control unit CU. For example, the CPU 13 switches
on/off the electronic switches of the high voltage input power supply
circuit 11 and the low voltage input power supply circuit 12. Further,
the CPU 13 supplies control signals to the battery units BU. The CPU 13
supplies to the battery units BU a control signal for turning on the
power supply to the battery units BU or a control signal for instructing
the battery units BU to charge or discharge. The CPU 13 can output
control signals of different contents to the individual battery units BU.

[0050] The CPU 13 is connected to a memory 15, a D/A (Digital to Analog)
conversion section 16, an A/D (Analog to Digital) conversion section 17
and a temperature sensor 18 through a bus 14. The bus 14 is configured,
for example, from an I2C bus. The memory 15 is configured from a
nonvolatile memory such as an EEPROM (Electrically Erasable and
Programmable Read Only Memory). The D/A conversion section 16 converts
digital signals used in various processes into analog signals.

[0051] The CPU 13 receives sensor information measured by the voltage
sensors and the current sensors. The sensor information is inputted to
the CPU 13 after it is converted into digital signals by the A/D
conversion section 17. The temperature sensor 18 measures an
environmental temperature. For example, the temperature sensor 18
measures a temperature in the inside of the control unit CU or a
temperature around the control unit CU.

[0052] The CPU 13 may have a communication function. For example, the CPU
13 and a personal computer (PC) 19 may communicate with each other. The
CPU 13 may communicate not only with the personal computer but also with
an apparatus connected to a network such as the Internet.

[Power Supply System of the Control Unit]

[0053] FIG. 3 principally shows an example of a configuration of the
control unit CU which relates to a power supply system. A diode 20 for
the backflow prevention is connected to the output stage of the high
voltage input power supply circuit 11. Another diode 21 for the backflow
prevention is connected to the output stage of the low voltage input
power supply circuit 12. The high voltage input power supply circuit 11
and the to voltage input power supply circuit 12 are connected to each
other by OR connection by the diode 20 and the diode 21. Outputs of the
high voltage input power supply circuit 11 and the low voltage input
power supply circuit 12 are combined and supplied to the battery unit BU.
Actually, that one of the outputs of the high voltage input power supply
circuit. 11 and the low voltage input power supply circuit 12 which
exhibits a higher voltage is supplied to the battery unit BU. However,
also a situation in which the electric power from both of the high
voltage input power supply circuit 11 and the low voltage input power
supply circuit 12 is supplied is entered in response to the power
consumption of the battery unit BU which serves as a load.

[0054] The control unit CU includes a main switch SW1 which can be
operated by a user. When the main switch SW1 is switched on, electric
power is supplied to the CPU 13 to start up the control unit CU. The
electric power is supplied to the CPU 13, for example, from a battery 22
built in the control unit CU. The battery 22 is a rechargeable battery
such as a lithium-ion battery. A DC voltage from the battery 22 is
converted into a voltage, with which the CPU 13 operates, by a DC-DC
converter 23. The voltage obtained by the conversion is supplied as a
power supply voltage to the CPU 13. In this manner, upon start-up of the
control unit CU, the battery 22 is used. The battery 22 is controlled,
for example, by the CPU 13.

[0055] The battery 22 can be charged by electric power supplied from the
high voltage input power supply circuit 11 or the low voltage input,
power supply circuit 12 or otherwise from the battery units BU. Electric
power supplied from the battery units BU is supplied to a charger circuit
24. The charger circuit 24 includes a DC-DC converter. The voltage V13
supplied from the battery units BU is converted into a DC voltage of a
predetermined level by the charger circuit 24. The DC voltage obtained by
the conversion is supplied to the battery 22. The battery 22 is charged
by the DC voltage supplied thereto.

[0056] It is to be noted that the CPU 13 may operate with the voltage V13
supplied thereto from the high voltage input power supply circuit 11, low
voltage input power supply circuit 12 or battery units BU. The voltage
V13 supplied from the battery units BU is converted into a voltage of a
predetermined level by a DC-DC converter 25. The voltage obtained by the
conversion is supplied as a power supply voltage to the CPU 13 so that
the CPU 13 operates.

[0057] After the control unit CU is started up, if at least one of the
voltages V10 and V11 is inputted, then the voltage V12 is generated. The
voltage V12 is supplied to the battery units BU through the electric
power line L1. At this time, the CPU 13 uses the signal line SL to
communicate with the batter's units BU. By this communication, the CPU 13
outputs a control signal for instructing the battery units BU to start up
and discharge. Then, the CPU 13 switches on a switch SW2. The switch SW2
is configured, for example, from an FET (Field Effect Transistor). Or the
switch SW2 may be configured from an IGBT (Insulated Gate Bipolar
Transistor). When the switch SW2 is on, the voltage V13 is supplied from
the battery units BU to the control unit CU.

[0058] A diode 26 for the backflow prevention is connected to the output
side of the switch SW2. The connection of the diode 26 can prevent
unstable electric power, which is supplied from a solar battery or a wind
power generation source, from being supplied directly to the external
apparatus. Thus, stabilized electric power supplied from the battery
units BU can be supplied to the external apparatus. Naturally, a diode
may be provided on the final stage of the battery units BU in order to
secure the safety.

[0059] In order to supply the electric power supplied from the battery
units BU to the external apparatus, the CPU 13 switches on a switch SW3.
When the switch SW3 is switched on, the voltage V14 based on the voltage
V13 is supplied to the external apparatus through the electric power line
P3. It is to be noted that the voltage V14 may be supplied to the other
battery units BU so that the batteries B of the other battery units BU
are charged by the voltage V14.

[Example of the Configuration of the High Voltage Input Power Supply
Circuit]

[0060] FIG. 4 shows an example of a particular configuration of the high
voltage input power supply circuit. Referring to FIG. 14, the high
voltage input power supply circuit 11 includes the DC-DC converter 11b
and a feedforward controlling system hereinafter described. In FIG. 4,
the voltage sensor 11c, electronic switch 11d, current sensor 11e,
current sensor 11f, electronic switch 11g and voltage sensor 11h as well
as the diode 20 and so forth are not shown.

[0061] The low voltage input power supply circuit 12 is configured
substantially similarly to the high voltage input power supply circuit 11
except that the DC-DC converter 12a is that of the step-up type.

[0062] The DC-DC converter 11b is configured from a primary side circuit
32 including, for example, a switching element, a transformer 33, and a
secondary side circuit 34 including a rectification element and so forth.
The DC-DC converter 11b shown in FIG. 4 is that of the current resonance
type, namely, an LLC resonance converter.

[0063] The feedforward controlling system includes an operational
amplifier 35, a transistor 36 and resistors Rc1, Rc2 and Rc3. An output
of the feedforward controlling system is inputted to a controlling
terminal provided on a driver of the primary side circuit 32 of the DC-DC
converter 11b. The DC-DC converter 11b adjusts the output voltage from
the high voltage input power supply circuit 11 so that the input voltage
to the controlling terminal may be fixed.

[0064] Since the high voltage input power supply circuit 11 includes the
feedforward controlling system, the output voltage from the high voltage
input power supply circuit 11 is adjusted so that the value thereof may
become a voltage value within a range set in advance. Accordingly, the
control unit CU including the high voltage input power supply circuit 11
has a function of a voltage conversion apparatus which varies the output
voltage, for example, in response to a change of the Input voltage from a
solar cell, or the like.

[0065] As seen in FIG. 4, an output voltage is extracted from the high
voltage input power supply circuit 11 through the AC-DC converter 11
including a capacitor 31, primary side circuit 32, transformer 33 and
secondary side circuit 34. The AC-DC converter 11 is a power factor
correction circuit disposed where the input to the control unit CU from
the outsiders an AC power supply.

[0066] The output from the control unit CU is sent to the battery units BU
through the electric power line L1. For example, the individual battery
units BUa, BUb and BUc are connected to output terminals Te1, Te2, Te3, .
. . through diodes D1, D2, D3, . . . for the backflow prevention,
respectively.

[0067] In the following, the feedforward controlling system provided in
the high voltage input power supply circuit 11 is described.

[0068] A voltage obtained by stepping down the input voltage to the high
voltage input power supply circuit 11 to kc times, where kc is
approximately one several tenth or one hundredth, is inputted to the
non-negated input terminal of the operational amplifier 35. Meanwhile, to
the negated input terminal c1 of the operational amplifier 35, a voltage
obtained by stepping down a fixed voltage Vt0 determined in advance
to kc times is inputted. The input voltage kc×Vt0 to the
negated input terminal c1 of the operational amplifier 35 is applied, for
example, from the D/A conversion section 16. The value of the voltage
Vt0 is retained in a built-in memory of the D/A conversion section
16 and can be changed as occasion demands. The value of the voltage
Vt0 may otherwise be retained into the memory 15 connected to the
CPU 13 through the bus 14 such that it is transferred to the D/A
conversion section 16.

[0069] The output terminal of the operational amplifier 35 is connected to
the base of the transistor 36, and voltage-current conversion is carried
out in response to the difference between the input voltage to the
non-negated input terminal and the input voltage to the negated input
terminal of the operational amplifier 35 by the transistor 36.

[0070] The resistance value of the resistor Rc2 connected to the emitter
of the transistor 36 is higher than the resistance value of the resistor
Rc1 connected in parallel to the resistor Rc2.

[0071] It is assumed that, for example, the input voltage to the rich
voltage input power supply circuit 11 is sufficiently higher than the
fixed voltage Vt0 determined in advance. At this time, since the
transistor 36 is in an on state, and the value of the combined resistance
of the resistor Rc1 and the resistor Rc2 is lower than the resistance
value of the resistor Rc1, the potential at a point f shown in FIG. 4
approaches the ground potential.

[0072] Consequently, the input voltage to the controlling terminal
provided on the driver of the primary side circuit 32 and connected to
the point f through a photo-coupler 37 drops. The DC-DC converter 11b
which detects the drop of the input voltage to the controlling terminal
steps up the output voltage from the high voltage input power supply
circuit 11 so that the input voltage to the controlling terminal may be
fixed.

[0073] It is assumed now that, for example, the terminal voltage of the
solar cell connected to the control unit CU drops conversely and the
input voltage to the high voltage input power supply circuit 11
approaches the fixed voltage Vt0 determined advance.

[0074] As the input voltage to the high voltage input power supply circuit
11 drops, the state of the transistor 36 approaches an off state from an
on state. As the state of the transistor 36 approaches an off state from
an on state, current becomes less likely to flow to the resistor Rc1 and
the resistor Rc2, and the potential at the point f shown in FIG. 4 rises.

[0075] Consequently, the input voltage to the controlling terminal
provided on the driver of the primary side circuit 32 is brought out of a
state in which it is kept fixed. Therefore, the DC-DC converter 11b steps
down the output voltage from the high voltage input power supply circuit
11 so that the input voltage to the controlling terminal may be fixed.

[0076] In other words, in the case where the input voltage is sufficiently
higher than the fixed voltage Vt0 determined advance, the high
voltage input power supply circuit 11 steps up the output voltage. On the
other hand, if the terminal voltage of the solar cell drops and the input
voltage approaches the fixed voltage Vt0 determined in advance, then
the high voltage input power supply circuit 11 steps down the output
voltage. In this manner, the control unit CU including the high voltage
input power supply circuit 11 dynamically changes the output voltage in
response to the magnitude of the input voltage.

[0077] Furthermore, as hereinafter described, the high voltage input power
supply circuit 11 dynamically changes the output voltage also in response
to a change of the voltage required on the output side of the control
unit CU.

[0078] For example, it is assumed that the number of those battery units
BU which are electrically connected to the control unit CU increases
during electric generation of the solar cell. In other words, it is
assumed that the load as viewed from the solar cell increases during
electric generation of the solar cell.

[0079] In this instance, a battery unit BU is electrically connected
additionally to the control unit CU, and consequently, the terminal
voltage of the solar cell connected to the control unit CU drops. Then,
when the input voltage to the high voltage input power supply circuit 11
drops, the state of the transistor 36 approaches an off state from an on
state, and the output voltage from the high voltage input power supply
circuit 11 is stepped down.

[0080] On the other hand, if it is assumed chat the number of those
battery units BU which are electrically connected to the control unit CU
decreases during electric generation of the solar cell, then the load as
viewed from the solar cell decreases. Consequently, the terminal voltage
of the solar cell connected to the control unit CU rises. If the input
voltage to the high voltage input power supply circuit 11 becomes
sufficiently higher than the fixed voltage Vt0 determined in
advance, then the input voltage to the controlling terminal provided on
the driver of the primary side circuit 32 drops. Consequently, the output
voltage from the high voltage input power supply circuit 11 is stepped
up.

[0081] It is to be noted that the resistance values of the resistors Rc1,
Rc2 and Rc3 are selected suitably such that the value of the output
voltage of the high voltage input power supply circuit 11 may be included
in a range set in advance. In other words, the upper limit to the output
voltage from the high voltage input power supply circuit 11 is determined
by the resistance values of the resistors Rc1 and Rc2. The transistor 36
is disposed so that, when the input voltage to the high voltage input
power supply circuit 11 is higher than the predetermined value, the value
of the output voltage from the high voltage input, power supply circuit
11 may not exceed the voltage value of the upper limit set in advance.

[0082] On the other hand, the lower limit to the output voltage from the
high voltage input power supply circuit 11 is determined by the input
voltage to the non-negated input terminal of an operational amplifier of
a feedforward controlling system of the charger circuit 41a as
hereinafter described.

[Internal Configuration of the Battery Unit]

[0083] FIG. 5 shows an example of an internal configuration of the battery
units BC. Here, description is given taking the battery unit BUa as an
example. Unless otherwise specified, the battery unit BUb and the battery
unit BUc have a configuration similar to that of the battery unit BUa.

[0084] Referring to FIG. 5, the battery unit BUa includes a charger
circuit 41a, a discharger circuit 42a and a battery Ba. The voltage V12
is supplied from the control unit CU to the charger circuit 41a. The
voltage V13 which is an output from the battery unit BUa is supplied to
the control unit CU through the discharger circuit 42a. The voltage V13
may otherwise be supplied directly to the external, apparatus from the
discharger circuit 42a.

[0085] The charger circuit 41a includes a DC-DC converter 43a. The voltage
V12 inputted to the charger circuit 41a is converted into a predetermined
voltage by the DC-DC converter 43a. The predetermined voltage obtained by
the conversion is supplied to the battery Ba to charge the battery Ba.
The predetermined voltage differs depending upon the type and so forth of
the battery Ba. To the input stage of the DC-DC converter 43a, a voltage
sensor 43b, an electronic switch 43c and a current sensor 43d are
connected. To the output stage of the DC-DC converter 43a, a current
sensor 43e, an electronic switch 43f and a voltage sensor 43g are
connected.

[0086] The discharger circuit 42a includes a DC-DC converter 44a. The DC
voltage supplied from the battery Ba to the discharger circuit 42a is
converted into the voltage V13 by the DC-DC converter 44a. The voltage
V13 obtained by the conversion is outputted from the discharger circuit
42a. To the input stage of the DC-DC converter 44a, a voltage sensor 44b,
an electronic switch 44c and a current sensor 44d are connected. To the
output stage of the DC-DC converter 44a, a current sensor 44e, an
electronic switch 44f and a voltage sensor 44g are connected.

[0087] The battery unit BUa includes a CPU 45. The CPU 45 controls the
components of the battery unit BU. For example, the CPU 45 controls
on/off operations of the electronic switches. The CPU 45 may carry out
processes for assuring the safety of the battery B such as an overcharge
preventing function and an excessive current preventing function. The CPU
45 is connected to a bus 46. The bus 46 may be, for example, an I2C
bus.

[0088] To the bus 46, a memory 47, an A/D conversion section 48 and a
temperature sensor 49 are connected. The memory 47 is a rewritable
nonvolatile memory such as, for example, an EEPROM. The A/D conversion
section 48 converts analog sensor information obtained by the voltage
sensors and the current sensors into digital information. The sensor
information converted into digital signals by the A/D conversion section
48 is supplied to the CPU 45. The temperature sensor 49 measures the
temperature at a predetermined place in the battery unit BU.
Particularly, the temperature sensor 49 measures, for example, the
temperature of the periphery of a circuit hoard on which the CPU 45 is
mounted, the temperature of the charger circuit 41a and the discharger
circuit 42a and the temperature of the battery Ba.

[Power Supply System of the Battery Unit]

[0089] FIG. 6 shows an example of a configuration of the battery unit BUa
principally relating to a power supply system. Referring to FIG. 6, the
battery unit BUa does not include a main switch. A switch SW5 and a DC-DC
converter 39 are connected between the battery Ba and the CPU 45. Another
switch SW6 is connected between the battery Ba and the discharger circuit
42a. A further switch SW7 is connected to the input stage of the charger
circuit 41a. A still further switch SW8 is connected to the output stage
of the discharger circuit 42a. The switches SW are configured, for
example, from an FET.

[0090] The battery unit BUa is started up, for example, by a control
signal from the control unit CU. A control signal, for example, of the
high level is normally supplied from the control unit CU to the battery
unit BUa through a predetermined signal line. Therefore, only by
connecting a port of the battery unit BUa to the predetermined signal
line, the control signal of the high level is supplied to the switch SW5
making the switch SW5 in an on state to start up the battery unit BUa.
When the switch SW5 is on, a DC voltage from the battery Ba is supplied
to the DC-DC converter 39. A power supply voltage for operating the CPU
45 is generated by the DC-DC converter 39. The generated power supply
voltage is supplied to the CPU 45 to operate the CPU 45.

[0091] The CPU 45 executes control in accordance with an instruction of
the control unit CU. For example, a control signal for the instruction to
charge is supplied from the control unit CU to the CPU 45. In response to
the instruction to charge, the CPU 45 switches off the switch SW6 and the
switch SW3 and then switches on the switch SW7. When the switch SW7 is
on, the voltage V12 supplied from the control unit CU is supplied to the
charger circuit 41a. The voltage V12 is converted into a predetermined
voltage nay the charger circuit 41a, and the battery Ba is charged by the
predetermined voltage obtained by the conversion. It is to be noted that
the charging method into the battery B can be changed suitably in
response to the type of the battery B.

[0092] For example, a control signal for the instruction to discharge is
supplied from the control unit CU to the CPU 45. In response to the
instruction to discharge, the CPU 45 switches off the switch SW7 and
switches on the switches SW6 and SW8. For example, the switch SW8 is
switched on after a fixed interval of time after the switch SW6 is
switched on. When the switch SW6 is on, the DC voltage from the battery
Ba is supplied to the discharger circuit 42a. The DC voltage from the
battery Ba is converted into the voltage V13 by the discharger circuit
42a. The voltage V13 obtained by the conversion is supplied to the
control unit CU through the switch 5W8. It is to be noted that, though
not shown, a diode may be added to a succeeding stage to the switch SW8
in order to prevent the output of the switch SW8 from interfering with
the output from a different one of the battery units BU.

[0093] It is to be noted that the discharger circuit 42a can be changed
over between on and off by control of the CPU 45. In this instance, an
ON/OFF signal line extending from the CPU 45 to the discharger circuit
42a is used. For example, a switch SW not shown is provided on the output
side of the switch SW6. The switch SW in this instance is hereinafter
referred to as switch SW10 taking the convenience in description into
consideration. The switch SW10 carries out changeover between a first
path which passes the discharger circuit 42a and a second path which does
not pass the discharger circuit 42a.

[0094] In order to turn on the discharger circuit 42a, the CPU 45 connects
the switch SWIG to the first path. Consequently, an output from the
switch. SW6 is supplied to the switch SW8 through the discharger circuit
42a. In order to turn off the discharger circuit 42a, the CPU 45 connects
the switch SW10 to the second path. Consequently, the cutout from the
switch SW6 is supplied directly to the switch SW8 without by way of the
discharger circuit 42a.

[Example of the Configuration of the Charger Circuit]

[0095] FIG. 7 shows an example of a particular configuration of the
charger circuit of the battery unit. Referring to FIG. 7, the charger
circuit 41a includes a DC-DC converter 43a, and a feedforward controlling
system and a feedback controlling system hereinafter described. It is to
be noted that in FIG. 7, the voltage sensor 43b, electronic switch 43c,
current sensor 43d, current sensor 43e, electronic switch 43f, voltage
sensor 43g, switch SW7 and so forth are not shown.

[0096] Also the charger circuits of the battery units BU have a
configuration substantially similar to that of the charger circuit 41a
shown in FIG. 7.

[0097] The DC-DC converter 43a is configured, for example, from a
transistor 51, a coil 52, a controlling IC (Integrated Circuit) 53 and so
forth. The transistor 51 is controlled by the controlling IC 53.

[0098] The feedforward controlling system includes an operational
amplifier 55, a transistor 56, and resistors Rb1, Rb2 and Rb3 similarly
to the high voltage input power supply circuit 11. An output of the
feedforward controlling system is inputted, for example, to a controlling
terminal provided on the controlling IC 53 of the DC-DC converter 43a.
The controlling IC 53 in the DC-DC converter 43a adjusts the output
voltage from the charger circuit 41a so that the input voltage to the
controlling terminal may be fixed.

[0099] In other words, the feedforward controlling system provided in the
charger circuit 41a acts similarly to the feedforward controlling system
provided in the high voltage input power supply circuit 11.

[0100] Since the charger circuit 41a includes the feedforward controlling
system, the output voltage from the charger circuit 41a is adjusted so
that the value thereof may become a voltage value within a range set in
advance. Since the value of the output voltage from the charger circuit
is adjusted to a voltage value within the range set in advance, the
charging current to the batteries B electrically connected to the control
unit CU is adjusted in response to a change of the input voltage from the
high voltage input power supply circuit 11. Accordingly, the battery
units BU which include the charger circuit have a function of a charging
apparatus which changes the charge rate to the batteries B.

[0101] Since the charge rate to the batteries B electrically connected to
the control unit CU is changed, the value of the input voltage to the
charger circuits of the battery units BU, or in other words, the value of
the output voltage of the high voltage input power supply circuit 11 or
the low voltage moot power supply circuit 12, is adjusted so as to become
a voltage value within the range set in advance.

[0102] The input to the charger circuit 41a is an output, for example,
from the high voltage input power supply circuit 11 or the low voltage
input power supply circuit 12 of the control, unit CU described
hereinabove. Accordingly, one of the output terminals Te1, Te2, Te3, . .
. shown in FIG. 4 and the input terminal of the charger circuit 41a are
connected to each other.

[0103] As seen in FIG. 7, an output voltage from the charger circuit. 41a
is extracted through the DG-DC converter 43a, a current sensor 54 and a
filter 59. The battery Ba is connected to a terminal Tb1 of the charger
circuit 41a. In other words, the output from the charger circuit 41a is
used as an input to the battery Ba.

[0104] As hereinafter described, the value of the output voltage from each
charger circuit is adjusted so as to become a voltage value within the
range set in advance in response to the type of the battery connected to
the charger circuit. The range of the output voltage from each charger
circuit is adjusted by suitably selecting the resistance value of the
resistors Rb1, Rb2 and Rb3.

[0105] Since the range of the output voltage from each charger circuit is
determined individually in response to the type of the battery connected
to the charger circuit, the type of the batteries B provided in the
battery units BU is not limited specifically. This is because the
resistance values of the resistors Rb1, Rb2 and Rb3 in the charger
circuits may be suitably selected in response to the type of the
batteries B connected thereto.

[0106] It is to be noted that, while the configuration wherein the output
of the feedforward controlling system is inputted to the controlling
terminal of the controlling IC 53 is shown in FIG. 7, the CPU 45 of the
battery units BU may supply an input to toe controlling terminal of the
controlling IC 53. For example, the CPU 45 of the battery unit BU may
acquire information relating to the input voltage to the battery unit BU
from the CPU 13 of the control unit CU through the signal line SL. The
CPU 13 of the control unit CU can acquire information relating to the
input voltage to the battery unit BU from a result of measurement of the
voltage sensor 11h or the voltage sensor 12g.

[0107] In the following, the feedforward controlling system provided in
the charger circuit 41a is described.

[0108] The input to the non-negated input terminal of the operational
amplifier 55 is a voltage obtained by stepping down the input voltage to
the charger circuit 41a to kb times, where kb is approximately one
several tenth to one hundredth. Meanwhile, the input to the negated input
terminal b1 of the operational amplifier 55 is a voltage obtained by
stepping down a voltage Vb, which is to be set as a lower limit to the
output voltage from the high voltage input power supply circuit 11 or the
low voltage input power supply circuit 12, to kb times. The input voltage
kb×Vb to the negated input terminal b1 of the operational amplifier
55 is applied, for example, from the CPU 45.

[0109] Accordingly, the feedforward controlling system provided in the
charger circuit 41a steps up the output voltage from the charger circuit
41a when the input voltage to the charger circuit 41a is sufficiently
higher than the fixed voltage Vb determined in advance. Then, when the
input voltage to the charger circuit 41a approaches the fixed voltage Vb
determined in advance, the feedforward controlling system steps down the
output voltage from the charger circuit 41a.

[0110] The transistor 56 is disposed so that, when the input, voltage to
the charger circuit 41a is higher than the predetermined value, the value
of the output voltage from the charger circuit 41a may not exceed an
upper limit set in advance similarly to the transistor 36 described
hereinabove with reference to FIG. 4. It is to be noted that the range of
the value of the output voltage from the charger circuit 41a depends upon
the combination of the resistance values of the resistors Rb1, Rb2 and
Rb3. Therefore, the resistance values of the resistors Rb1, Rb2 and Rb3
are adjusted in response to the type of the batteries B connected to the
charger circuits.

[0111] Further, the charger circuit 41a includes also the feedback
controlling system as described hereinabove. The feedback controlling
system is configured, for example, from a current sensor 54, an
operational amplifier 57, a transistor 58 and so forth.

[0112] If the current amount supplied to the battery Ba exceeds a
prescribed value set in advance, then the output voltage from the charger
circuit 41a is stepped down by the feedback controlling system, and the
current amount supplied to the battery Ba is limited. The degree of the
limitation to the current amount to be supplied to the battery Ba is
determined in accordance with a rated value of the battery B connected to
each charger circuit.

[0113] If the output voltage from the charger circuit 41a is stepped down
by the feedforward controlling system or the feedback controlling system,
then the current amount to be supplied to the battery Ba is limited. When
the current amount supplied to the battery Ba is limited, as a result,
charging into the battery Ba connected to the charger circuit 41a is
decelerated.

[0114] Now, in order to facilitate understandings of the embodiment of the
present disclosure, a control method is described taking the MPPT control
and control by the voltage tracking method as an example.

[MPPT Control]

[0115] First, an outline of the MPPT control is described below.

[0116]FIG. 8A is a graph illustrating a voltage-current characteristic of
a solar cell. In FIG. 8A, the axis or ordinate represents the terminal
current of the solar cell, and the axis of abscissa represents the
terminal voltage of the solar cell. Further, in FIG. 8A, Isc represents
an output current value when the terminals of the solar cell are
short-circuited while light is irradiated upon the solar cell, and Voc
represents an output voltage when the terminals of the solar cell are
open while light is irradiated upon the solar cell. The current Isc and
the voltage Voc are called short-circuit current and open-circuit
voltage, respectively.

[0117] As seen in FIG. 8A, when light is irradiated upon the solar cell,
the terminal current of the solar cell indicates a maximum value when the
terminals of the solar cell are short-circuited. At this time, the
terminal voltage of the solar cell is almost 0. On the other hand, when
light is irradiated upon the solar cell, the terminal voltage of the
solar cell exhibits a maximum value when the terminals of the solar cell
are open. At this time, the terminal current of the solar cell is
substantially 0 A.

[0118] It is assumed now that the graph indicative of a voltage-current
characteristic of the solar cell is represented by a curve C1 shown in
FIG. 8A. Here, if a load is connected to the solar cell, then the voltage
and current to be extracted from the solar cell depend upon the power
consumption required by the load connected to the solar cell. A point on
the curve C1 represented by a set of the terminal voltage and the
terminal current of the solar cell at this time is called operating point
of the solar cell. It is to be noted that FIG. 8A schematically indicates
the position of the operating point but does not indicate the position of
an actual operating point. This similarly applies also to an operating
point appearing on any other figure of the present disclosure.

[0119] If the operating point is changed on the curve representative of a
voltage-current characteristic of the solar cell, then a set of a
terminal voltage Va and terminal current Ia with which the product of the
terminal voltage and the terminal current, namely, the generated electric
power, exhibits a maximum value, is found. The point represented the set
of the terminal voltage Va and the terminal current Ia with which the
electric power obtained by the solar cell exhibits a maximum value is
called optimum operating point of the solar cell.

[0120] When the graph indicative of a voltage-current characteristic of
the solar cell is represented by the curve C1 illustrated in FIG. 8A, the
maximum electric power obtained from the solar cell is determined by the
product of the terminal voltage Va and the terminal current Ia which
provide the optimum operating point. In other words, when the graph
indicating a voltage-current characteristic of the solar cell is
represented by the curve C1 illustrated in FIG. 8A, the maximum electric
power obtained from the solar cell is represented by the area of a
shadowed region an FIG. 8A, namely by Va×Ia. It is to be noted that
the amount obtained, by dividing Va×Ia by Voc×Isc is a fill
factor.

[0121] The optimum operating point varies depending upon the electric
power required by the load connected to the solar cell, and the point
PA representative of the operating point moves on the curve C1 as
the electric power required by the load connected to the solar cell
varies. When the electric power amount required by the load is small, the
current to be supplied to the load may be lower than the terminal current
at the optimum operating point. Therefore, the value of the terminal
voltage of the solar cell at this time is higher than the voltage value
at the optimum operating point. On the other hand, when the electric
power amount required by the load is greater than the electric power
amount which can be supplied at the optimum operating point, the electric
power amount exceeds the electric power which can be supplied at the
illumination intensity at this point of time. Therefore, it is considered
that the terminal voltage of the solar cell drops toward 0 V.

[0122] Curves C2 and C3 shown in FIG. 8A indicate, for example,
voltage-current characteristics of the solar cell when the illumination
intensity upon the solar cell varies. For example, the curve C2 shown in
FIG. 8A corresponds to the voltage-current characteristic in the case
where the illumination intensity upon the solar cell increases, and the
curve C3 shown in FIG. 8A corresponds to the voltage-current
characteristic in the case where the illumination intensity upon the
solar cell decreases.

[0123] For example, lithe illumination intensity upon the solar cell
increases and the curve representative of the voltage-current
characteristic of the solar cell changes from the curve C1 to the curve
C1, then also the optimum operating point varies in response to the
increase of the illumination intensity upon the solar cell. It is to be
noted that the optimum operating point at this time moves from a point on
the curve C1 to another point on the curve C2.

[0124] The MPPT control is nothing but to determine an optimum operating
point with respect to a variation of a curve representative of a
voltage-current characteristic of the solar cell and control the terminal
voltage or terminal current of the solar cell so that electric power
obtained from the solar cell may be maximized.

[0125]FIG. 8B is a graph, namely, a P-V curve, representative of a
relationship between the terminal voltage of the solar cell and the
generated electric power of the solar cell in the case where a
voltage-current characteristic of the solar cell is represented by a
certain curve.

[0126] If it is assumed that the generated electric power of the solar
cell assumes a maximum value Pmax at the terminal voltage at which the
maximum operating point is provided as seen in FIG. 8B, then the terminal
voltage which provides the maximum operating point can be determined by a
method called mountain climbing method. A series of steps described below
is usually executed by a CPU or the like of a power conditioner connected
between the solar cell and the power system.

[0127] For example, the initial value of the voltage inputted from the
solar cell is set to V0, and the generated electric power P0 at
this time is calculated first. Then, the voltage to be inputted from the
solar cell is incremented by ε, which is greater than 0, namely,
ε>0 to determine the voltage V1 as represented by
V1=V0+ε. Then, the generated electric power P1
when the voltage inputted from the solar cell is V1 is calculated.
Then, the generated electric powers P0 and P1 are compared with
each other, and if P1>P0, then the voltage to be inputted
from the solar cell is incremented by ε as represented by
V2=V1+ε. Then, the generated electric power P2
when the voltage inputted from the solar cell is V2 is calculated.
Then, the resulting generated electric power P2 is compared with the
formerly generated electric power P1. Then, if P2>P1,
then the voltage to be inputted from the solar cell is incremented by
ε as represented by V3=V2+ε. Then, the
generated electric power P3 when the voltage inputted from the solar
cell is V3 is calculated.

[0128] Here, if P3<P2, then the terminal voltage which
provides the maximum operating point exists between the voltages V2
and V3. By adjusting the magnitude of ε in this manner, the
terminal voltage which provides the maximum operating point can be
determined with an arbitrary degree of accuracy. A bisection method
algorithm may be applied to the procedure described above. It is to be
noted that, if the P-V curve has two or more peaks in such a case that a
shade appears locally on the light irradiation face of the solar cell,
then a simple mountain climbing method cannot cope with this. Therefore,
the control program requires some scheme.

[0129] According to the MPPT control, since, the terminal voltage can be
adjusted such that the load as viewed from the solar cell is always in an
optimum state, maximum electric power can be extracted from the solar
cell in different weather conditions. On the other hand, analog/digital
conversion (A/D conversion) is required for calculation of the terminal
voltage which provides the maximum operating point and besides
multiplication is included in the calculation. Therefore, time is
required for the control. Consequently, the MPPT control cannot sometimes
respond to a sudden chance of the illumination intensity upon the solar
cell in such a case that the sky suddenly becomes cloudy and the
illumination intensity upon the solar cell changes suddenly.

[Control by the Voltage Tracking Method]

[0130] Here, if the curves C1 to C3 shown in FIG. 8A are compared with
each other, then the change of the open voltage Voc with respect to the
change of the illumination intensity upon the solar cell, which may be
considered a change of a curve representative of a voltage-current
characteristic, is smaller than the change of the short-circuit current
Isc. Further, all solar cells indicate voltage-current characteristics
similar to each other, and it is known that, in the case of a crystal
silicon solar cell, the terminal voltage which provides the maximum
operating point is found around approximately 80% of the open voltage.
Accordingly, it is estimated that, if a suitable voltage value is set as
the terminal voltage of the solar cell and the output current of a
converter is adjusted so that the terminal voltage of the solar cell
becomes equal to the set voltage value, then electric power can be
extracted efficiently from the solar cell. Such control by current
limitation as just described is called voltage tracking method.

[0131] In the following, an outline of the control by the voltage tracking
method is described. It is assumed that, as a premise, a switching
element is disposed between the solar cell and the power conditioner and
a voltage measuring instrument is disposed between the solar cell and the
switching element. Also it is assumed that: the solar cell is in a state
in which light is irradiated thereon.

[0132] First, the switching element is switched off, and then when
predetermined time elapses, the terminal voltage of the solar cell is
measured by the voltage measuring instrument. The reason Why the lapse of
the predetermined time is waited before measurement of the terminal
voltage of the solar cell after the switching off of the switching
element is that it is intended to wait that the terminal voltage of the
solar cell is stabilized. The terminal voltage at this time is the open
voltage Voc.

[0133] Then, the voltage value of, for example, 80% of the open voltage
Voc obtained by the measurement is calculated as a target voltage value,
and the target voltage value is temporarily retained into a memory or the
like. Then, the switching element is switched on to start energization of
the converter in the power conditioner. At this time, the output current
of the converter is adjusted so that the terminal voltage of the solar
cell becomes equal to the target voltage value. The sequence of processes
described above is executed after every arbitrary interval of time.

[0134] The control by the voltage tracking method is high in loss of the
electric power obtained by the solar cell in comparison with the MPPT
control. However, since the control by the voltage tracking method can be
implemented by a simple circuit and is lower in cost, the power
conditioner including the converter can be configured at a comparatively
low cost.

[0135]FIG. 9A illustrates a change of the operating point with respect to
a change of a curve representative of a voltage-current characteristic of
the solar cell. In FIG. 9A, the axis of ordinate represents the terminal
current of the solar cell, and the axis of abscissa represents the
terminal voltage of the solar cell. Further, a blank round mark in FIG.
9A represents the operating point when the MPPT control is carried out,
and a solid round mark in FIG. 9A represents the operating point when
control by the voltage tracking method is carried out.

[0136] It is assumed now that the curve representative of a
voltage-current characteristic of the solar cell is a curve C5. Then, if
it is assumed that, when the illumination intensity upon the solar cell
changes, the curve representative of the voltage-current characteristic
of the solar cell successively changes from the curve C5 to a curve C8.
Also the operating points according to the control methods change in
response to the change of the curve representative of the voltage-current
characteristic of the solar cell. It is to be noted that, since the
change of the open voltage Voc with respect to the change of the
illumination intensity upon the solar cell is small, in FIG. 9A, the
target voltage value when control by the voltage tracking method is
carried out is regarded as a substantially fixed value Vs.

[0137] As can be seen from FIG. 9A, when the curve representative of the
voltage-current characteristic of the solar cell is a curve C6, the
degree of the deviation between the operating point of the MPPT control
and the operating point of the control by the voltage tracking method is
low. Therefore, it is considered that, when the curve representative of
the voltage-current characteristic of the solar cell is the curve C6,
there is no significant difference in generated electric power obtained
by the solar cell between the two different controls.

[0138] On the other hand, if the curve representative of the
voltage-current characteristic of the solar cell is the curve C8, then
the degree of the deviation between the operating point of the MPPT
control and the operating point of the control by the voltage tracking
method is high. For example, if the differences ΔV6 and ΔV8
between the terminal voltage when the MPPT control is applied and the
terminal voltage when the control by the voltage tracking method is
applied, respectively, are compared with each other as seen in FIG. 9A,
then ΔV6<ΔV8. Therefore, when the curve representative of
the voltage-current characteristic of the solar cell is the curve C8, the
difference between the generated electric power obtained from the solar
cell when the MPPT control is applied and the generated electric power
obtained from the solar cell when the control by the voltage tracking
method is applied is great.

[Cooperation Control of the Control Unit and the Battery Unit]

[0139] Now, an outline of cooperation control of the control unit and the
battery unit is described. In the following description, control by
cooperation or Interlocking of the control unit and the battery unit is
suitably referred to as cooperation control.

[0140] FIG. 95 shows an example of a configuration of a control system
wherein cooperation control by a control unit and a plurality of battery
units is carried out.

[0141] Referring to FIG. SB, for example, one or a plurality of battery
units BU each including a set of a charger circuit and a battery are
connected to the control unit CU. The one or plural battery units BU are
connected in parallel to the electric power line L1 as shown in FIG. 9B.
It is to be noted that, while only one control unit CU is shown in FIG.
9B, also in the case where the control system includes a plurality of
control units CU, one or a plurality of control units CU are connected in
parallel to the electric power line L1.

[0142] Generally, if it is tried to use electric power obtained by a solar
cell to charge one battery, then the MPPT control or the control by the
voltage tracking method described above is executed by a power
conditioner interposed between the solar cell and the battery. Although
the one battery may be configured from a plurality of batteries which
operate in an integrated manner, usually the batteries are those of the
single type. In other words, it is assumed that the MPPT control or the
control by the voltage tracking method described above is executed by a
single power conditioner connected between a solar cell and one battery.
Further, the number and configuration, which is a connection scheme such
as parallel connection or series connection, of batteries which make a
target of charging do not change but are fixed generally during charging.

[0143] In the meantime, in the cooperation control, the control unit CU
and the plural battery units BUa, BUb, BUc, . . . carry out autonomous
control so that the output voltage of the control unit CU and the voltage
required by the battery units BU are balanced well with each other. As
described hereinabove, the batteries B included in the battery units BUa,
BUb, BUc, . . . may be of any types. In other words, the control unit CU
according to the present disclosure can carry out cooperation control for
a plurality of types of batteries B.

[0144] Further, in the configuration example shown in FIG. 9B, the
individual battery units BU can be connected or disconnected arbitrarily,
and also the number of battery units BU connected to the control unit CU
is changeable during electric generation of the solar cell. In the
configuration example shown in FIG. 9B, the load as viewed from the solar
cell is variable during electric generation of the solar cell. However,
the cooperation control can cope not only with a variation of the
illumination intensity on the solar cell but also with a variation of the
load as viewed from the solar cell during electric generation of the
solar cell. This is one of significant characteristics which are not
achieved by configurations in related arts.

[0145] It is possible to construct a control system which dynamically
changes the charge rate in response to the supplying capacity from the
control unit CU by connecting the control unit CU and the battery units
BU described above to each other. In the following, an example of the
cooperation control is described. It is to be noted that, although, in
the following description, a control system wherein, in an initial state,
one battery unit BUa is connected to the control unit CU is taken as en
example, the cooperation control applies similarly also where a plurality
of battery units BU are connected to the control unit CU.

[0146] It is assumed that, for example, the solar cell is connected to the
input side of the control unit CU and the battery unit BUa is connected
to the out side of the control unit CU. Also it is assumed that the upper
limit to the output voltage of the solar cell is 100 V and the lower
limit to the output voltage of the solar cell is desired to be suppressed
to 75 V. In other words, it is assumed that the voltage Vt0 is set
to Vt0=75 V and the input voltage to the negated input terminal of
the operational, amplifier 35 is kc×75 V.

[0147] Further, it is assumed that the upper limit and the lower limit to
the output voltage from the control unit CU are set, for example, to 48 V
and 45 V, respectively, in other words, it is assumed that the voltage Vb
is set to Vb=45 V and the input voltage to the negated input terminal of
the operational amplifier 55 is kb×45 V. It is to be noted that the
value of 48 V which is the upper limit to the output terminal from the
control unit CU is adjusted by suitably selecting the resistors Rc1 and
Rc2 in the high voltage input power supply circuit 11. In other words, it
is assumed that the target voltage value of the output from the control
unit CU is set to 48 V.

[0148] Further, it is assumed that the upper limit and the lower limit to
the output voltage from the charger circuit 41a of the battery unit BUa
are set, for example, to 42 V and 26 V, respectively. Accordingly, the
resistors Rb1, Rb2 and Rb3 in the charger circuit 41a are selected so
that the upper limit and the lower limit to the output voltage from the
charger circuit 41a may become 42 V and 28 V, respectively.

[0149] It is to be noted that a state in which the input voltage to the
charger circuit 41a is the upper limit voltage corresponds to a state in
which the charge rate into the battery Ba is 100% whereas another state
in which the input voltage to the charger circuit 41a is the lower limit
voltage corresponds to a state in which the charge rate is 0%. In
particular, the state in which the input voltage to the charger circuit
41a is 48 V corresponds to the state in which the charge rate into the
battery Ba is 100%, and the state in which the input voltage to the
charger circuit 41a is 45 V corresponds to the state in which the charge
rate into the battery Ba is 0%. In response to the variation within the
range of the input voltage, from 45 to 48 V, the charge rate is set
within the range of 0 to 100%.

[0150] It is to be noted that charge rate control into the battery may be
carried out in parallel to and separately from the cooperation control.
In particular, since constant current charging is carried out at an
initial stage of charging, the output from the charger circuit 41a is
feedback-adjusted to adjust the charge voltage so that the charge current
may be kept lower than fixed current. Then at a final stage, the charge
voltage is kept equal to or lower than a fixed voltage. The charge
voltage adjusted here is equal to or lower than the voltage adjusted by
the cooperation control described above. By the control, a charging
process is carried out within the electric power supplied from the
control unit CU.

[0151] First, a change of the operating point when the cooperation control
is carried out in the case where the illumination intensity upon the
solar cell changes is described.

[0152] FIG. 10A illustrates a change of the operating point when the
cooperation control is carried out in the case where the illumination
intensity upon the solar cell decreases. In FIG. 10A, the axis of
ordinate represents the terminal current of the solar cell and the axis
of abscissa represents the terminal, voltage of the solar cell. Further,
a blank round mark in FIG. 10A represents an operating point when the
MPPT control is carried out, and a shadowed round mark in FIG. 10A
represents an operating point when the cooperation control is carried
out. Curves C5 to C8 shown in FIG. 10A represent voltage-current
characteristics of the solar cell when the illumination intensity upon
the solar cell changes.

[0153] It is assumed now that the electric power required by the battery
Ba is 100 W (watt) and the voltage current characteristic of the solar
cell is represented by the curve C5 which corresponds to the most sunny
weather state. Further, it is assumed that the operating point of the
solar cell at this time is represented, for example, by a point a on the
curve C5, and the electric power or supply amount supplied from the solar
cell to the battery Ba through the high voltage input power supply
circuit 11 and the charger circuit 41a is higher than the electric power
or demanded amount required by the battery Ba.

[0154] When the electric power supplied from the solar cell to the battery
Ba is higher than the electric power required by the battery Ba, the
output voltage from the control unit CU to the battery unit BUa, namely
the voltage V12, is 48 V of the upper limit. In particular, since the
input voltage to the battery unit BUa is 48 V of the upper the limit, the
output voltage from the charger circuit 41a of the battery unit BUa is 42
V of the upper limit, and charge into the battery Ba is carried out at
the charge rate of 100%. It is to be noted that surplus electric power is
abandoned, for example, as heat. It is to be noted that, although it has
been described that the charge into the battery is carried out at 100%,
the charge into the battery is not limited to 100% but can be adjusted
suitably in accordance with a characteristic of the battery.

[0155] If the sky begins to become cloudy from this state, then the curve
representative of the voltage-current characteristic of the solar cell
changes from the curve C5 to the curve C6. As the sky becomes cloudy, the
terminal voltage of the solar cell gradually drops, and also the output
voltage from the control unit CU to the battery unit BUa gradually drops.
Accordingly, as the curve representative of the voltage-current
characteristic of the solar cell changes from the curve C5 to the curve
C6, the operating point of the solar cell moves, for example, to a point
b on the curve C6.

[0156] If the sky becomes cloudier from this state, then the curve
representative of the voltage-current characteristic of the solar cell
changes from the curve C6 to the curve C7, and as the terminal voltage of
the solar cell gradually drops, also the output voltage from the control
unit CU to the battery unit BUa drops. When the output voltage from the
control unit CU to the battery unit BUa drops by some degree, the control
system cannot supply the electric power of 100% to the battery Ba any
more.

[0157] Here, if the terminal voltage of the solar cell approaches
Vt0=75 V of the lower limit from 100 V, then the high voltage input
power supply circuit 11 of the control unit CU begins to step down the
output voltage to the battery unit BUa from 48 V toward Vb 45 V.

[0158] After the output voltage from the control unit CU to the battery
unit BUa begins to drop, the input voltage to the battery unit BUa drops,
and consequently, the charger circuit 41a of the battery unit BUa begins
to step down the output voltage to the battery Ba. When the output
voltage from the charger circuit 41a drops, the charge current supplied
to the battery Ba decreases, and the charging into the battery Ba
connected to the charger circuit 41a is decelerated. In other words, the
charge rate into the battery Ba drops.

[0159] As the charge rate to the battery Ba drops, the power consumption,
decreases, and consequently, the load as viewed from the solar cell
decreases. Consequently, the terminal, voltage of the solar cell rises or
recovers by the decreased amount of the load as viewed from the solar
cell.

[0160] As the terminal voltage of the solar cell rises, the degree of the
drop of the output voltage from the control unit CU to the battery unit
BUa decreases and the Input voltage to the battery unit BUa rises. As the
input voltage to the battery unit BUa rises, the charger circuit 41a of
the battery unit BUa steps up the output voltage from the charger circuit
41a to raise the charge rate into the battery Ba.

[0161] As the charge rate into the battery Ba rises, the load as viewed
from the solar cell increases and the terminal voltage of the solar cell
drops by the increased amount of the load as viewed from the solar cell.
As the terminal voltage of the solar cell drops, the high voltage input
power supply circuit 11 of the control unit CU steps down the output
voltage to the battery unit BUa.

[0162] Thereafter, the adjustment of the charge rate described above is
repeated automatically until the output voltage from the control unit CU
to the battery unit BUa converges to a certain value to establish a
balance between the demand and the supply of the electric power.

[0163] The cooperation control is different from the MPPT control in that
it is not controlled by software. Therefore, the cooperation control does
not require calculation of the terminal voltage which provides a maximum
operating point. Further, the adjustment of the charge rate by the
cooperation control does not include calculation by a CPU. Therefore, the
cooperation control is low in power consumption in comparison with the
MPPT control, and also the charge rate adjustment described above is
executed in such a short period of time of approximately several
nanoseconds to several hundred nanoseconds.

[0164] Further, since the high voltage input power supply circuit 11 and
the charger circuit 41a merely detect the magnitude of the input voltage
thereto and adjust the output voltage, analog/digital conversion is not
required and also communication between the control unit CU and the
battery unit BUa is not required. Accordingly, the cooperation control
does not require complicated circuitry, and the circuit for implementing
the cooperation control is small in scale.

[0165] Here, it is assumed that, at the point a on the curve C5, the
control unit CU can supply the electric power of 100 W and the output
voltage from the control unit CU to the battery unit BUa converges to a
certain value. Further, it is assumed that the operating point of the
solar cell changes, for example, to the point c on the curve C7. At this
time, the electric power supplied to the battery Ba becomes lower than
100 W. However, as seen in FIG. 10A, depending upon selection of the
value of the voltage Vt0, electric power which is not inferior to
that in the case wherein the MPPT control is carried out can be supplied
to the battery Ba.

[0166] If the sky becomes further cloudy, then the curve representative of
the voltage-current characteristic of the solar cell changes from the
curve C7 to the curve C8, and the operating point of the solar cell
changes, for example, to a point d on the curve C8.

[0167] As seen in FIG. 10A, since, under the cooperation control, the
balance between the demand and the supply of electric power is adjusted,
the terminal voltage of the solar cell does not become lower than the
voltage Vt0. In other words, under the cooperation control, even if
the illumination intensity on the solar cell drops extremely, the
terminal voltage of the solar cell does not become lower than the voltage
Vt0 at all.

[0168] If the illumination intensity on the solar cell drops extremely,
then the terminal voltage of the solar cell comes to exhibit a value
proximate to the voltage Vt0, and the amount of current supplied to
the battery Ba becomes very small. Accordingly, when the illumination
intensity on the solar cell drops extremely, although time is required
for charging of the battery Ba, since the demand and the supply of
electric power in the control system are balanced well with each other,
the control system does not suffer from the system down.

[0169] Since the adjustment of the charge rate by the cooperation control
is executed in very short time as described above, according to the
cooperation control, even if the sky suddenly begins to become cloudy and
the illumination intensity on the solar cell decreases suddenly, the
system down of the control system can be avoided.

[0170] Now, a change of the operating point when the cooperation control
is carried out in the case where the load as viewed, from the solar cell,
changes is described.

[0171] FIG. 10B illustrates a change of the operating point when the
cooperation control is carried out in the case where the load as viewed
from the solar cell increases. In FIG. 10B, the axis of ordinate
represents the terminal current of the solar cell and the axis of
abscissa represents the terminal voltage of the solar cell. Further, a
shadowed round mark in FIG. 10B represents an operating point when the
cooperation control is carried out.

[0172] It is assumed now that the illumination intensity on the solar cell
does not change and the voltage-current characteristic of the solar cell
is represented by a curve C0 shown in FIG. 10B.

[0173] Immediately after the control system is started up, it estimates
that the power consumption in the inside thereof is almost zero, and
therefore, the terminal voltage of the solar cell may be considered
substantially equal to the open voltage. Accordingly, the operating point
of the solar cell immediately after the startup of the control system may
be considered existing, for example, at a point e on the curve C0. It is
to be noted that the output voltage from the control unit CU to the
battery unit BUa may be considered to be 48 V of the upper limit.

[0174] After supply of electric power to the battery Ba connected to the
battery unit BUa is started, the operating point of the solar cell moves,
for example, to a point g on the curve C0. It is to be noted that since,
in the description of the present example, the electric power required by
the battery Ba is 100 W, the area of a region S1 indicated by a shadow in
FIG. 10B is equal to 100 W.

[0175] When the operating point of the solar cell is at the point g on the
curve C0, the control system is in a state in which the electric power
supplied from the solar cell to the battery Ba through the high voltage
input power supply circuit 11 and the charger circuit 41a is higher than
the electric power required by the battery Ba. Accordingly, the terminal
voltage of the solar cell, the output voltage from the control unit CU
and the voltage supplied to the battery Ba when the operating point of
the solar cell is at the point g on the curve C0 are 100 V, 48 V and 42
V, respectively.

[0176] Here, it is assumed that the battery unit BUb having a
configuration similar to that of the battery unit BUa is newly connected
to the control unit CU. If it is assumed that the battery Bb connected to
the battery unit BUb requires electric power of 100 W for the charge
thereof similarly to the battery Ba connected to the battery unit BUa,
then the power consumption increases and the load as viewed from the
solar cell increases suddenly.

[0177] In order to supply totaling electric power of 200 W to the two
batteries, the totaling output current must be doubled, for example,
while the output voltage from the charger circuit. 41a of the battery
unit BUa and the charger circuit 41b of the battery unit BUb is
maintained.

[0178] However, where the power generator is the solar cell, also the
terminal voltage of the solar cell drops together with increase of output
current from the charger circuits 41a and 41b. Therefore, the totaling
output current must be higher than twice in comparison with that in the
case when the operating point of the solar cell is at the point g.
Therefore, the operating point of the solar cell must be, for example, at
a point h on the curve C0 as shown in FIG. 10B, and the terminal voltage
of the solar cell drops extremely. If the terminal voltage of the solar
cell drops extremely, then the control system may suffer from system
down.

[0179] In the cooperation control, if the terminal voltage of the solar
cell, drops as a result of new or additional connection of the battery
unit BUb, then adjustment of the balance between the demand and the
supply of electric power in the control system is carried out. In
particular, the charge rate into the two batteries is lowered
automatically so that electric power supplied to the battery Ba and the
battery Bb may totally become, for example, 15.0 W.

[0180] In particular, if the terminal voltage of the solar cell drops as a
result of new connection of the battery unit BUb, then also the output
voltage from the control unit CU to the battery units BUa and BUb drops.
If the terminal voltage of the solar cell approaches Vt0=75 V of the
lower limit from 100 V, then the high voltage input power supply circuit
11 of the control unit CU begins to step down the output voltage to the
battery units BUa and BUb toward Vb=45 V from 48 V.

[0181] As the output voltage from the control unit CU to the battery units
BUa and BUb is stepped down, the input voltage to the battery units BUa
and BUb drops. Consequently, the charger circuit 41a of the battery unit
BUa and the charger circuit 41b of the battery unit BUb begin to step
down the output voltage to the batteries Ba and Bb, respectively. As the
output voltage from the charger circuit drops, the charging into the
batteries connected to the charger circuit is decelerated. In other
words, the charge rate to each battery is lowered.

[0182] As the charge rate into each battery is lowered, the power
consumption decrease as a whole, and consequently, the load as viewed
from the solar cell decreases and the terminal voltage of the solar cell
rises or recovers by an amount corresponding to the decreasing amount of
the load as viewed from the solar cell.

[0183] Thereafter, adjustment of the charge rate is carried out until the
output voltage from the control unit CU to the battery units BUa and BUb
converges to a certain value to establish a balance between the demand
and the supply of electric power in a similar manner as in the case where
the illumination intensity on the solar cell decreases suddenly.

[0184] It is to be noted that it depends upon the situation to which value
the voltage value actually converges. Therefore, although the value to
which the voltage value actually converges is not, known clearly, since
charging stops when the terminal voltage of the solar cell becomes equal
to Vt0=75 V of the lower limit, it is estimated that the voltage
value converges to a value a little higher than the value of Vt0 of
the lower limit. Further, it is estimated that, since the individual
battery units are not controlled in an interlocking relationship with
each other, even if the individual battery units have the same
configuration, the charge rate differs among the individual battery units
due to a dispersion of used elements. However, there is no change in that
the battery units can generally be controlled by the cooperation control.

[0185] Since the adjustment of the charge rune by the cooperation control
is executed in a very short period of time, if the battery unit BUb is
connected newly, then the operating point of the solar cell changes from
the point g to a point i on the curve C0. It is to be noted that, while a
point h is illustrated as an example of the operating point of the solar
cell on the curve C0 for the convenience of description in FIG. 10B,
under the cooperation control, the operating point of the solar cell does
not actually chance to the point h.

[0186] In this manner, in the cooperation control, the charger circuit of
the individual battery units BU detects the magnitude of the input
voltage thereto in response to an increase of the load as viewed from the
solar cell, and automatically suppresses the current amount to be sucked
thereby. According to the cooperation control, even if the number of
those battery units BU which are connected to the control unit CU
increases to suddenly increase the load as viewed from the solar cell,
otherwise possible system down of the control system can be prevented.

[0187] Now, a change of the operating point when the cooperation control
is carried out in the case where both of the illumination intensity on
the solar cell and the load as viewed from the solar cell vary is
described.

[0188] FIG. 11 illustrates a change of the operating point when the
cooperation control is carried out in the case where both of the
illumination intensity on the solar cell and the load as viewed from the
solar cell vary. In FIG. 11, the axis of ordinate represents the terminal
current of the solar cell and the axis of abscissa represents the
terminal voltage of the solar cell. A shadowed round mark in FIG. 11
represents an operating point when the cooperation control is carried
out. Curves C5 to C8 shown in FIG. 11 indicate voltage-current
characteristics of the solar cell in the case where the illumination
intensity upon the solar cell varies.

[0189] First, it is assumed that the battery unit BUa which includes the
battery Ba which requires the electric power of 100 W for the charging
thereof is connected to the control unit CU. Also it is assumed that the
voltage-current characteristic of the solar cell at this time is
represented by a curve C7 and the operating point of the solar cell is
represented by a point p on the curve C7.

[0190] It is assumed that the terminal voltage of the solar cell at the
point p considerably approaches the voltage Vt0 set in advance as a
lower limit to the output voltage of the solar cell. That the terminal
voltage of the solar cell considerably approaches the voltage Vt0
signifies that, in the control system, adjustment of the charge rate by
the cooperation control is executed and the charge rate is suppressed
significantly. In particular, in the state in which the operating point
of the solar cell is represented by the point p shown in FIG. 11, the
electric power supplied to the battery Ba through the charger circuit 41a
is considerably higher than the electric power supplied to the high
voltage input power supply circuit 11 from the solar cell. Accordingly,
in the state in which the operating point of the solar cell is
represented by the point p shown in FIG. 11, adjustment of the charge
rate is carried out by a great amount, and electric power considerably
lower than 100 W is supplied to the charger circuit 41a which charges the
battery Ba.

[0191] It is assumed that the illumination intensity upon the solar cell
thereafter increases and the curve representative of the voltage-current
characteristic of the solar cell changes from the curve C7 to the curve
C6. Further, it is assumed that the battery unit BUb which has a
configuration similar to that of the battery unit BUa is newly connected
to the control unit CU. At this time, the operating point of the solar
cell changes, for example, from the point p on the curve C7 to a point q
on the curve C6.

[0192] Since the two battery units are connected to the control unit CU,
the power consumption when the charger circuits 41a and 41b fully charge
the batteries Ba and Bb is 200 W. However, when the illumination
intensity upon the solar cell is not sufficient, the cooperation control
is continued and the power consumption is adjusted to a value lower than
200 W such as, for example, to 150 W.

[0193] It is assumed here that the sky thereafter clears up and the curve
representative of the voltage-current characteristic of the solar cell
changes from the curve C6 to the curve C5. At this time, when the
generated electric power of the solar cell increases together with the
increase of the illumination intensity upon the solar cell, the output
current from the solar cell increases.

[0194] If the illumination intensity upon the solar cell increases
sufficiently and the generated electric power of the solar cell, further
increases, then the terminal voltage of the solar cell becomes
sufficiently higher than the voltage Vt0 at a certain point. If the
electric power supplied from the solar cell to the two batteries through
the high voltage input power supply circuit 11 and the charger circuits
41a and 41b comes to be higher than the electric power required to charge
the two batteries, then the adjustment of the charge rate by the
cooperation control, is moderated or automatically cancelled.

[0195] At this time, the operating point of the solar cell is represented,
for example, by a point r on the curve C5 and charging into the
individual batteries Ba and Bb is carried out at the charge rate of 100%.

[0196] Then, it is assumed that the illumination intensity upon the solar
cell decreases and the curve representative of the voltage-current
characteristic of the solar cell changes from the curve C5 to the curve
C6.

[0197] When the terminal voltage of the solar cell drops and approaches
the voltage Vt0 set in advance, the adjustment of the charge rate by
the cooperation control is executed again. The operating point of the
solar cell at this point of time is represented by a point q of the curve
C6.

[0198] It is assumed that the illumination intensity on the solar cell
thereafter decreases further and the curve representative of the
voltage-current characteristic of the solar cell changes from the curve
C6 to the curve C8.

[0199] Consequently, since the charge rate is adjusted so that the
operating point of the solar cell may not become lower than the voltage
Vt0, the terminal current from the solar cell decreases, and the
operating point of the solar cell changes from the point q on the curve
C6 to a point s on the curve C8.

[0200] In the cooperation control, the balance between the demand and the
supply of electric power between the control unit CU and the individual
battery units BU is adjusted so that the input voltage to the individual
battery units BU may not become lower than the voltage Vt0
determined in advance. Accordingly, with the cooperation control, the
charge rate into the individual batteries B can be changed on the real
time basis in response to the supplying capacity of the input side as
viewed from the individual battery units BU. In this manner, the
cooperation control can cope not only with a variation of the
illumination intensity on the solar cell but also with a variation of the
load as viewed from the solar cell.

[0201] As described hereinabove, the present disclosure does not require a
commercial power supply. Accordingly, the present disclosure is effective
also in a district in which a power supply apparatus or electrical power
network is not maintained.

[Unit Number Controlling Process]

[0202] Now, a unit number controlling process is described. The unit
number controlling process is a process of changing the number of battery
units for which a charging process is to be carried out. FIG. 12
illustrates a voltage-current characteristic when the illumination
intensity on the solar cell varies. FIG. 12 illustrates a change of the
operating point when the number of battery units to be charged is also
changed.

[0203] It is assumed that, in a sunny weather state, the voltage-current
characteristic of the solar cell is represented, for example, by a curve
C5. When the number of battery units for which a charging process is to
be carried out is 0, the operating point is a point aa. As the number of
battery units for which a charging process is to be carried out
increases, the current flowing through the battery units increases. For
example, if a charging process for a first battery unit is started, then
the operating point moves from the point as to another point bb. Then, if
a charging process for a second battery unit is started, then the
operating point moves from the point bb to a further point cc. Then, if a
charging process for a third battery unit is started, then the operating
point moves from the point cc to a still, further point dd.

[0204] On the other hand, it is assumed that, in a cloudy weather state,
the voltage-current characteristic of the solar cell is represented, for
example, by a curve C8. When the number of battery units for which a
charging process is to be carried out is 0, the operating point is a
point ee. As the number of battery units for which a charging process is
to be carried out increases, the current flowing through the battery
units increases. For example, if a charging process for a first battery
unit is started, then the operating point moves from the point ee to
another point ff. Then, if a charging process for a second battery unit
is started, then the operating point moves from the point if to a further
point gg. Here, if the voltage V becomes equal to or comes near to the
voltage Vt0, then the cooperation control described hereinabove is
rendered operative. Therefore, even if the number of units for which a
charging process is to be carried out is increased to three units, the
operating point little moves on the curve C8. The operating point at this
point of time is represented by a point gg'. The positions of the
operating points gg and gg' are almost same as each other. However, at
the operating point gg, a charging process is carried out for two battery
units. At the operating point gg', a charging process is carried out such
that electric power when charging is carried out for two units is
distributed to three battery units.

[0205] Here, the output by the photovoltaic power generation varies
depending upon the weather. Naturally, not only in the photovoltaic power
generation but also in wind power generation or manpower generation, the
output varies depending upon the situation. When the output of the
electric power generation section varies in this manner, it can become a
subject in what manner the number of battery units for which a charging
process is to be carried out is changed. For example, when the operating
point moves from the pint dd to the point gg', it is necessary to
determine whether or not the number of units is to be decreased to move
the operating point to the point gg.

[0206] As one method, it seems a possible idea to change the number of
units in response to a change in weather. For example, in a sunny weather
state, the number of buttery units for which a charging process is to be
carried out is successively increased from one to two or three. Then, if
the weather becomes cloudy, the charging process for the third unit is
stopped to decrease the number of battery units for which a charging
process is to be carried out to two. However, the change in weather lacks
in regularity. Particularly in such a weather that a sunny weather and a
cloudy weather repeat alternately, the process of starting and stopping
the charging process for the third battery unit is repeated. Such a state
as just described imposes a burden on the battery or the charger circuit
of the third battery unit, and this is unfavorable. Therefore, in the
embodiment of the present disclosure, the following unit number
controlling process is carried out.

[First Unit Number Controlling Process]

[0207] FIG. 13 is a flow chart illustrating an example of a flow of
processing of a first unit number controlling process. Unless otherwise
specified, the processes described below are carried out by the CPU 13 of
the control unit CU. Referring to FIG. 13, after the first unit number
controlling process is started, first at step S1, an order in or ranks by
which the battery units are to be charged are determined such that a
battery unit for which a charging process is to be carried out may have
priority. Particularly, the ranking is carried out such that, for
example, a battery unit which has a comparatively low remaining capacity
or has comparatively high chargeability may have priority. It is assumed
here that the highest priority or rank is provided to the battery unit
BUa; the second highest priority or rank is provided to the battery unit
BUb; and the third highest priority or rank is provided to the battery
unit BUc. Then, the processing advances to step S2.

[0208] At step S2, it is decided whether or not an input from an electric
power generation section is received. The electric power generation
section generates electric power by photovoltaic power generation, wind
power generation or human power generation as described hereinabove. If
an input from the electric power generation section is not received, then
the process at step S2 is repeated. If an input from the electric power
generation section is received, then the processing advances to step S3.
The input from the electric power generation section is supplied to the
high voltage input power supply circuit 11 or the low voltage input power
supply circuit 12 of the control unit CU. A voltage supplied from the
electric power generation section to the control unit CU is suitably
referred to as received power voltage. The received power voltage
fluctuates by a variation of a state such as, for example, a change in
weather.

[0209] At step S3, the high voltage input power supply circuit 11 is
started up. Depending con the electric power generation section which
supplies the voltage, the low voltage input power supply circuit 12 is
stared up. Then, the processing advances to step S4.

[0210] At step S4, a battery unit BU is selected. For example, from among
the battery units ranked by the process at step S1, a battery of the
first rank is selected. Here, the battery unit BUa is selected. Then, the
processing advances to step S5. Au step S5, a charging instruction is
issued to the battery unit BUa. The charging instruction is provided from
the control unit CU to the battery unit BUa. The battery unit BUa starts
a charging process in response to the charging instruction. It is to be
noted that details of the process of starting charging into a battery
unit BU and the process of stopping the charging in response to an
instruction from the control unit CU have been described hereinabove, and
therefore, overlapping description of them is omitted herein to avoid
redundancy. Then, the processing advances to step S6.

[0211] At step S6, it is decided whether or not the received power voltage
is higher than a threshold value. It is to be noted that the condition of
the comparison may be set so as to permit the case where the received
power voltage is equal to the threshold value. The threshold value is
set, for example, to a value obtained by adding an offset of
approximately several volts to the value of the voltage Vt0, which
is 75 V. For example, the threshold value is set to approximately 78 V.
If the received power voltage is higher than the threshold value, then
the processing advances to step S7.

[0212] That the received power voltage is higher than the threshold value
signifies that the supply amount from the electric power generation
section is greater than the demand amount. Therefore, at step S7, the
number of those battery units which are to be charged is increased. It is
to be noted that the number of the battery units to be charged is
hereinafter referred to suitably as charging target unit number. Here,
since the charging process is being carried out already for the battery
unit BUa of the first rank, a charging instruction is issued to the
battery unit BUb of the second rank at step S7. A charging process for
the battery unit BUb is started in response to the charging instruction.
Then, the processing returns to step S6. Thus, when the received power
voltage is higher than the threshold value, a charging instruction is
successively issued to a battery unit BU in accordance with the rank
determined at step S1.

[0213] If the received power voltage is equal to or lower than the
threshold value at step S6, then the processing advances to step S8. At
step S8, it is decided whether or not a state in which the received power
voltage is equal to or lower than the threshold value continues for a
predetermined period of time. The predetermined period of time is set,
for example, to approximately several minutes to 10 minutes. If the state
in which the received power voltage is equal to or lower than the
threshold value does not continue for the predetermined period of time,
then the processing returns to step S6.

[0214] If the state in which the received power voltage is equal to or
lower than the threshold value continues for the predetermined period of
time, then the processing advances to step S9. That the received power
voltage is equal to or lower than the threshold value signifies that the
demand amount by the battery unit is equal to or greater than the supply
amount from the electric power generation section. Therefore, at step S9,
the charging process by the battery unit whose charging process was
started last is stopped. Then, the processing returns to step S6.

[0215] In this manner, in the first unit number controlling process, even
when the received power voltage is equal to or lower than the threshold
value, the charging target unit number is not decreased immediately. The
charging target unit number is decreased after it is decided that the
predetermined period of time elapses. Consequently, for example, even if
the weather changes from a sunny weather to a cloudy weather and then
changes back to a sunny weather before long, the unit number is not
changed. In particular, such a situation that starting and stopping of a
charging process of a certain battery unit are repeated frequently can be
prevented.

[0216] Before the process at step S7 is carried out, a process similar to
that carried out at step S8 may be carried out. However, when the supply
amount from the electric power generation section is greater than the
demand amount by the battery unit, in order to efficiently use the supply
amount from the electric power generation section, preferably the
charging target unit number is increased without waiting lapse of the
predetermined period of time. If lapse of the predetermined period of
time is decided in only one of the process of increasing the charging
target unit number and the process of decreasing the charging target unit
number, then such a situation that starting and stopping of a charging
process into the battery unit BU are repeated frequently can be
prevented.

[0217] It is to be noted that, in the comparison with the threshold value
at step S6, a threshold value may be used which is different depending
upon whether the charging target unit number is to be increased or
decreased. When the unit number is to be increased, the threshold value
is set, for example, to approximately 78 V. When the unit number is to be
decreased, the threshold value is preferably set to a value of the volts
e Vt0, for example, 75 V or to approximately 75.5 V which is a
little higher than the voltage Vt0.

[Second Unit Number Controlling Process]

[0218] Now, a second unit number controlling process is described. In
order to facilitate understandings of the second unit number controlling
process, description is given using a particular example. It is to be
noted that, in the particular example, it is assumed that charge power
for the battery units is 100 W. For example, the supply amount from the
solar cell is 210 W.

[0219] FIG. 14 illustrates a first particular example. Referring to FIG.
14, when a charging process for two battery units BU is being carried
out, the supply amount, which is 210 W, exceeds the demand amount, which
is 200 W for the two battery units BU. Accordingly, the cooperation
control does not operate but is off. At this time, 10 W from within the
supply amount is not used but becomes a loss. It is assumed that electric
power of 12 W is consumed by the charger circuit 41 in each of the
battery units BU. In this instance, the electric power actually charged
into the two battery units is 200 W-24 W, which is electric power
consumed by the two charger circuits, and hence is 176 W. The electric
power actually used for the charge is hereinafter referred to as
effective charge power.

[0220] Since the supply amount of the photovoltaic power generation
exceeds the demand amount by the battery unit side, in a usual case, the
charging target unit number is increased. However, the second unit number
controlling process carries out control so that electric power from the
electric power generation section can be used more efficiently taking the
power consumption by the charger circuit into consideration.

[0221] For example, it is assumed that the charging target unit number is
increased to three. In this instance, since the demand amount by the
battery unit side, which is 300 W, exceeds the supply amount from the
photovoltaic power generation, which is 210 W, the cooperation control is
turned on. The supply amount of the photovoltaic power generation is all
used as the charge power. Therefore, no loss occurs. In this instance,
the effective charge power is 210 W-36 W, which is electric power
consumed by the three charger circuits, and hence is 171 W.

[0222] If the effective charge powers in both cases are compared with each
other, then the effective charge power of 176 W represents efficient use
of the supply amount of the photovoltaic power generation. In such a
case, the charging target unit number is not increased but remains two.
If the charging target unit number at present is three, then the charging
target unit number is decreased to two.

[0223]FIG. 15 illustrates a second particular example. Referring to FIG.
15, when a charging process for two battery units BU is being carried
out, the supply amount, which is 210 W, exceeds the demand amount, which
is 200 W, because the two battery units BU are involved. Accordingly, the
cooperation control does not operate but is off. At this time, 10 W from
within the supply amount is not used but becomes a loss.

[0224] The power consumption of the charger circuit 41 sometimes differs
among different batteries of the battery units BU. While, in the first,
particular example, electric power of 12 W is consumed by the charger
circuit 41, it is assumed that, in the second particular example, the
charger circuit 41 consumes electric power of 8 W. In this instance, the
electric power actually charged into the two battery units is 200 W-16 W,
which is power consumption by the two charger circuits, and hence is 184
W.

[0225] Since the supply amount of the photovoltaic power generation
exceeds the demand amount by the battery unit side, usually the number of
charging target units is increased. However, the second unit number
controlling process carries out control so that electric, power from the
electric power generation section can be used more efficiently taking the
power consumption by the charger circuit into consideration.

[0226] For example, it is assumed that the charging target unit number is
increased to three. In this instance, since the demand amount by the
battery unit side, which is 300 W, exceeds the supply amount from the
photovoltaic power generation, which is 210 W, the cooperation control is
turned on. All of the supply amount of the photovoltaic power generation
is used as charge power. Therefore, no loss occurs. In this instance, the
effective charge power is 210 W-24 W, which is electric power consumed by
the three charger circuits, and hence is 186 W.

[0227] If the effective charge powers in both cases are compared with each
other, then the effective charge power of 186 W represents more efficient
use of the supply amount from the photovoltaic power generation. In such
an instance, the charging target unit number is increased to three. If
the charging target unit number at present is three, then it is not
decreased bat is maintained. In this manner, electric power supplied from
the photovoltaic power generation is used efficiently taking the power
consumption of the charger circuits into consideration.

[0228] The supply amount from the photovoltaic power generation sometimes
varies. For example, the sky clears up and the supply of the photovoltaic
power generation described above, which is 210 W, increases to 220 W. In
this instance, the effective charge power when the charging target unit
number is two is 200 W-24 W and hence is 176 W. On the other hand, the
effective charge power when the charging target unit number is three is
220 W-36 W and hence is 184 W. Consequently, the efficiency is higher
where the charging target unit number is three, and therefore, the
charging target unit number is increased to three from two. Or, the
charging target unit number is left three but is not decreased. In this
manner, also in a case in which the supply amount from the photovoltaic
power generation varies, the charging target unit number can be set
appropriately by carrying out comparison between the effective charge
powers.

[0229] It is to be noted that the power consumption may differ among
different charger circuits of the battery units. Also in this instance,
since the total power consumption of the charger circuits can be
calculated, the effective charge power can be determined.

[0230] FIG. 16 is a flow chart illustrating an example of a flow of the
second unit number controlling process. Referring to FIG. 16, at step S11
after the second unit number controlling process is started, it is waited
that a predetermined period of time elapses. The predetermined period of
time is set, for example, to substantially several minutes. After the
predetermined period of time elapses, the processing advances to step
S12.

[0231] At step S12, measurement of the received power voltage and the
current value is carried out, and the measured received power voltage and
current value are recorded. Then, the processing advances to step S13. At
step S13, it is decided whether or not a received power voltage and a
current value have been recorded by a predetermined number of times. If a
received power voltage and a current value have not been recorded by the
predetermined number of times, then the processing returns to step S11.
Then, after the predetermined period of time elapses, the measurement and
recording of a received power voltage and a current value are carried out
again. If a received power voltage and a current value have been recorded
by the predetermined number of times, then the processing advances to
step S14.

[0232] At step S14, a voltage-current characteristic, namely, a V-I curve,
of the photovoltaic power generation is estimated. Then, the processing
advances to step S15. At step S15, it is decided whether or not the
cooperation control is on. This decision is made through comparison
between the received power voltage and a threshold value. If the received
power voltage (supply) is equal to or lower than the threshold value
(demand), then it is decided that the cooperation control is on, and the
processing advances to step S16. However, if the received power voltage
is higher than the threshold value, then it is decided that the
cooperation control is off, and the processing advances to step S20. The
threshold value is set to the voltage Vt0 or a value a little higher
than the voltage Vt0.

[0233] That the cooperation control is on signifies that the demand amount
of the battery unit is equal to or exceeds the supply amount from the
photovoltaic power generation. Accordingly, the processes at step S16 are
those for deciding whether or not the charging target unit number into be
decreased.

[0234] At step S16, charge power when the charging target unit number is
decreased is calculated. For example, in the first particular example of
FIG. 14, the charge power when the charging target unit number is
decreased from three to two is calculated as 200 W. Then, the processing
advances to step S17. At step S17, the difference between the supply
power at present from the photovoltaic power generation and the electric
power calculated at step S16 is calculated. Then, an absolute value of
the difference is calculated. The absolute value of the difference is
suitably referred to as difference power. If it is assumed that the
supply power at present from the photovoltaic power generation is 210 W,
then the difference power is 210 W-200 W and therefore is calculated as
10 W. Then, the processing advances to step S18.

[0235] At step S18, the difference power and the power consumption by the
charger circuit are compared with each other. In the first particular
example, the power consumption of the charger circuit per one unit is 12
W. Therefore, the decision at step S18 is NO, and the processing returns
to step S11. In other words, the charging target unit number is not
decreased. In the case where the power consumption by the charger circuit
per one unit is 8 W as in the case of the second particular example
described hereinabove, the processing advances to step S19, at which a
process of decreasing the charging target unit number is carried out.
Then, the processing returns to step S11.

[0236] That the decision at step S15 is that the cooperation control is
off signifies that the supply amount from the photovoltaic power
generation exceeds the demand amount by the battery unit. Accordingly,
the processes at the steps beginning with step S20 decide whether or not
the charging target unit number should be increased.

[0237] At step S20, surplus electric power is calculated. The surplus
electric power is excessive electric power, for example, until the
cooperation control is carried out. In the first particular example of
FIG. 14, where the charging target unit number is two, the charge power
is 200 W. If the charging target unit number increases to three, then the
cooperation control is carried out, and therefore, the surplus electric
power is calculated as 10 W. Then, the processing advances to step S21.

[0238] At step S21, the surplus electric power and the power consumption
by the charger circuit are compared with each other. In the first
particular example, the power consumption by the charger circuit per one
unit is 12 W. Therefore, the decision at step S21 is NO, and the
processing returns to step S11. In other words, the charging target unit
number is not increased. In the case where the power consumption by the
charger circuit per one unit is 8 W similarly as in the case of the
second particular example described hereinabove, the processing advances
to step S22. At step S22, a process of increasing the charging target
unit number is carried out. Then, the processing returns to step S11.

[0239] As described, above, the number of battery units for which a
charging process is to be carried out is changed taking, for example, the
power consumption of the charger circuit into consideration.
Consequently, the electric power supplied from the electric power
generation section can be used to efficiently carry out charge into the
battery units.

[0240] The first and second unit number controlling processes described
hereinabove may be executed in combination. For example, the processes at
steps S16 to S19 may be carried out between the steps 28 and 59, and the
processes at steps S20 to S22 may be carried out between the steps S6 and
S7. The processes at steps S11 to S14 may be carried out in advance.

2. Modifications

[0241] Although the embodiment of the present disclosure has been
described, the present disclosure is not limited to the embodiment
described above but can be modified in various forms. All of the
configurations, numerical values, materials and so forth in the present
embodiment are mere examples, and the present disclosure is not limited
to the configurations and so forth given as the examples. The
configurations and so forth given as the examples can be suitably changed
within a range within which no technical contradiction occurs.

[0242] The control unit and the battery unit in the control system may be
portable. The control system described above may be applied, for example,
to an automobile or a house.

[0243] It is to be noted that the present disclosure may have such
configurations as described below.

(1)

[0244] A control apparatus, including:

[0245] a supplying section to which a voltage which varies in response to
a variation of a state is supplied from an electric power generation
section; and

[0246] a control section configured to change the number of battery units,
for which charging is to be carried out, in response to a relationship
between the voltage and a reference value.

(2)

[0247] The control apparatus according to (1), wherein the control section
increases the number of battery units when the voltage is higher than the
reference value but decreases the number of battery units when a state in
which the voltage is equal to or lower than the reference value continues
for a predetermined period of time.

(3)

[0248] The control apparatus according to (1), wherein the control section
calculates first electric power when the voltage is equal to or lower
than the reference value and decreases the number of battery units when
the first electric power is higher than power consumption of a charging
controlling section which the battery units have, and

[0249] calculates second electric power when the voltage is higher than
the reference value and increases the number of battery units when the
second electric power is higher than the power consumption of the
charging controlling section which the battery units have.

(4)

[0250] The control apparatus according to (3), wherein

[0251] the first electric bower is a difference between the electric power
supplied from the electric bower generation section and total electric
power of the battery units when the number of battery units is decreased,
and

[0252] the second electric power is a difference between the power
supplied form the electric power generation section and the total
electric power by the battery units.

(5)

[0253] The control apparatus according to any one of (1) to (4), wherein
the electric power generation section is configured from a photovoltaic
power generation section.

(6)

[0254] A control method, including:

[0255] supplying a voltage, which varies in response to a variation of a
state, from an electric power generation section; and

[0256] changing the number of battery units, for which charging is to be
carried out, in response to a relationship between the voltage and a
reference value.

[0257] The present disclosure contains subject matter related to that
disclosed in Japanese Priority Patent Application JP 2011-244038 filed in
the Japan Patent Office on Nov. 7, 2011, the entire content of which is
hereby incorporated by reference.